In other words, voters who can watch the whole bloody business live-streamed to their smartphones will be too squeamish to licence their politicians and generals to continue politics by violent means. He also worries that “outcomes are not as obvious perhaps in terms of defeat and victory.”

Gen Wall meanwhile says an interconnected world economy will further dissuade us from war: "Coming to a consensus for how you use hard power when it might affect your energy and your economy is going to be incredibly difficult."

The generals aren’t alone in this worry. Philip Hammond, now Foreign Secretary, publicly fretted while he was at the Ministry of Defence that the British public was war-weary and would not countenance any major military action after the Afghan mission winds down this year.

These are good and persuasive arguments and perhaps we should hope that they’re right: war is dreadful and – in almost every case – worse than the alternative course of action. Certainly, there’s evidence that Western electorates are in no hurry to pay the human or financial price for military action abroad these days. I’ve made those arguments myself, too.

And yet, I wonder. What if the generals, and petty scribblers like me, are making the eternal mistake of concluding that This Time Is Different?

Most periods of conflict are followed by the belief that peace – or at least, the absence of war – has become the norm. Many perfectly serious people believed – or at least, hoped – that Waterloo and the fall of Napoleon in 1815 would bring lasting peace to Europe. And yes, it took until 1870 for the next major conflict between the big European powers, but the 19th century was hardly peaceful. Britain fought in Crimea despite highly sophisticated and well-informed “audiences” at home. The first war correspondents kept public and Parliament informed, ensuring both debated the conflict extensively and energetically. The Earl of Aberdeen, the prime minister who took Britain into that war, was ousted before it ended as a result.

US Army helicopters cover the advance of South Vietnamese ground troops

Over the water, the US Civil War hardly fits the template of a simple, old-fashioned conflict suggested by today’s generals. Again, there were informed and articulate “audiences” whose views could and did determine military strategy and tactics: politics and public opinion leading up to 1864 Presidential election were arguably more important to the outcome of the war than any battle. As for Gen Carter’s “obvious outcomes”, neither side was fighting for outright victory but for the best deal in what everyone accepted would be a messy and painful settlement.

On the economic point made by Gen Wall, in the years before the First World War, there were perfectly good arguments that international trade and economic interdependence made war futile because it was in no one’s best interests. Norman Angell, who set out this case in the Great Illusion, is now unfairly being remembered as arguing WWI was impossible. He didn’t; he just said that it would be a very stupid thing to do.

Once that war broke out, it wasn’t long before people started talking about it as the last war, “the war to end war”, to use a phrase employed by everyone from HG Wells to Woodrow Wilson. Even before it ended, and long before 1939, the slogan had been discredited and was being used ironically.

Have we really moved on from war, entered an era when conflict is unacceptable and unsellable? It’s a lovely idea, and one that rests on the supposition that today we are so much more civilised and rational and informed than those who went before us. And indeed, humanity does indeed progress and life does indeed get better, cleaner, smarter and more productive.

The American Civil War

But then, since we crawled out of the oceans, pretty much every generation has told itself it is cleverer and better than its parents, and assured itself: we won’t make the same mistakes they did. Anyone who is honest with themselves knows what follows that conceit: a range of brand new mistakes we can then pass on to our children. Who knows if our collective unwillingness to act in Syria or Ukraine will led to greater horrors for which our successors will eventually damn us?

Such war tourism is hardly new: British and Russian aristocrats spectated on various Crimean battles from safe vantage points. Mark Twain even led a tour party to Crimea during the war. In the opening days of the US Civil War, Washington society gathered in Centreville, Virginia, for picnics to watch the First Battle of Bull Run.

War is horrible and costly and awful and stupid. But in a complicated world, it’s seductively simple. And perhaps most important of all, it’s also very exciting. Pretty much every war in the last couple of centuries was popular when it started, even though that popularity is often deliberately overlooked in later years. That’s even true of the most divisive conflicts of recent years, Vietnam and Iraq. For all the revisionist angst over those wars, remember that Richard Nixon, George W Bush and Tony Blair were all re-elected.

Robert E Lee, the general and devout Christian who nearly achieved a very different outcome to the US Civil War, said: “It is well that war is so terrible, otherwise we should grow too fond of it.”

A devout Christian who had seen – and caused – more slaughter than almost any other man of his age, Lee was acknowledging a lasting truth about humanity and warfare. The absence of war is only ever likely to be temporary.